Electric signal detector



Jan. 19, 1965 D. J. MORRIS 3,166,677

ELECTRIC SIGNAL DETECTOR Filed April 5Q 1961 Inventor D. I MOR'R 1.5

ttorneys 3,166,677 ELECTRIC SIGNAL DETECTOR David J. Morris, Beeston, Nottingham, England, assignor to Ericsson Telephones Limited, London, England, a British company Filed Apr. 5,1961, Ser. No. 100,922 Claims priority, application Great Britain, May 5, 1960, 15,858/60 Claims. (Cl. 307-88) ,This invention relates to electric signal detectors.

According to the invention there is provided an electric signal detector capable of stability in each of two alternative states and responsive to the application of a control signal to change from a first to a second of said states and to the termination of the control signal to revert from the second to the first state, in which an output signal con- United States Patent 0 sisting of a single output pulse of relatively significant amplitude is delivered when a change of state occurs and output pulses of only relatively insignificant amplitude are delivered while the detector attains stability in the state to which it has been changed.

The invention is particularly useful in eliminating the effects known as contact bounce when an electromagnetic relay is used to supply an input signal to apparatus responsive to pulse signals of short duration, e.g. electronic computers. The invention is also useful to give an output pulse signal whose duration or pulse width is small in comparison with the time required for the relay to operate, the output signal being delivered when the moving contact arm of the relay first makes contact with the terminal or contact stud towards which it is moving. 7 v

The invention will be described with reference to the accompanying drawings in which:

*FIGURE 1 shows a simple embodiment of the invention;

FIGURE 2 shows a hysteresis loop used in explaining the working of the embodiment of FIGURE 1, FIGURE 3 shows a modification to the embodiment of FIGURE "1. I Referring to FIGURE 1 a relay -A/-1, energisable on depression of a push-button :14, has a change-over contact arm a1 capable of connecting a common terminal-3 alternately to first andsecond terminals 1, 2. The terminals 2, '1 are connected to earth respectively by windings 4, 5 and series resistors 6, 7, the windings 4, 5 being wound in opposite senses on an annular .core 8'of magnetic material having a substantially rectangular hysteresis loop. Al-so wound on the core 8 is an output winding 9 connected to output terminals 10. The common terminal 3 is connected at supply terminal 11 to a voltage source of -V volts. 7 v

FIGURE 2 shows the hysteresis loop of the core 8. -With the contact arm ml in the position shown in FIG- 1 URE 1, current hows from earth to terminal '11 through resistor 7 and winding 5. This current is suificient to maintain the core 8' at the point C on the hysteresis loop of FIGURE. 2, ie at or near saturation in the sense shown by the arrow in FIGURE '1. When the push-button 14 is depressed, the relay-A/-'1 is energised and the contact arm a1 moves away from terminal :1. This interrupts the current flowing in the winding 5, and the core 8 assumes a remanent condition at or near the point D (FIGURE 2). As soon as the arm a1 reaches terminal Z, current flows from earth to terminal 11 through resistor 6 and winding 4. This current brings the core 8 to or near saturation in the sense opposite to the arrow in FIGURE 1, as represented by the point E (FIGURE 2). The change in the sense of magnetisation of the core 8 entails a relatively large change of flux, as represented by the distance parallel to the vertical axis between the points D and E of the hysteresis loop. This changein flux induces in the output winding 9 a single output pulse the amplitude of which corresponds to the flux change DE. This pulse is delivered to the output terminals '10 as the output pulse signal.

If now the contact arm a1 bounces and leaves the terminal 2, the current in winding 4 is interrupted until the arm returns to the terminal 2. During this interruption the condition of the core 8 changes, moving away from saturation or near-saturation at the point B towards the remanent condition represented by the point P. The extent of this change depends on the duration of the interruption, but the maximum change that can occur is limited to the value represented by the distance parallel to the vertical axis between the points E and F of the hysteresis loop. Since the loop is substantially rectangular this distance is insignificant in relation to the vertical distance DE. Hence at the beginning of the interruption a pulse is generated in the output winding 9 due to the flux change EF, and at the end of the intenruption an equal and opposite pulse due to the Ltiux change FE. Since both these changes are insignificant in relation to the change DE, the amplitude of both the resulting pulses is small and insignificant in relation to the amplitude of the single output pulse signal generated when the sense of magnetisation of the core 8 is changed. That is to say, the pulses caused by interruption arising from bouncing of the contact arm al are insignificant and may be neglected.

If the resistance R of the resistors 6, 7 is large compared to the impedance of the windings 4, 5 the current in the windings will have the value V /R which is constant. This value must be sufiicient to change the sense of magnetisation in the core 3.

When the push-button 14 is released, the relay A/1 is de-energised and the contact arm a1 moves from the terminal 2 to the terminal 1. In these circumstances similar considerations to those already described are applicable, an output pulse signal being delivered at the output terminals 10 of opposite polarity to'that deliveredwhen the button "14 was depressed. As an alternative, two output windings each in series with a rectifier may be provided so that unidirectional output signals are generated in each of the windings alternately.

-A second electromagnet could, if desired, be employed to give a positive return action to the contact arm :11. Other variations are possible, and the relay A/ l and its contact arm a l may be substituted by any suitable device which requires time to achieve stability in the state to which it is changed. For example, the arm almight be i 1, 2 may be outlets of a static switching device which is not immediately stable in the state to which it is changed.

The description given in connection with FIGURES 1, 2 assumes that the current in the windings 4, 5 has a constant value during switching of the core 8, i.e. while the sense of magnetisation of the core 8 isbeing changed. A more sharply defined output pulse signal is delivered at the output terminals 10 if the voltage across the windings, 4, 5 is maintained constant during the switching period. A modification of the circuit of FIGURE 1 by which this can be achieved is shown in FIGURE 3.

The circuit shown in FIGURE 3 is the circuit of FIG- URE 1 to which a potential of V vol-ts is applied through diodes 1-2, 13 to the points G, H at the ends of the windings 4, 5 remote from the contact arm a1 and the source of potential V 'volts. The value of V is less negative than V While the core 8 is being switched, the winding 4 or 5 which carries the switching current has a high impedance. The diodes 12, 13 are poled so as to maintain the potential at points G, H respectively at 'V.,, volts under these circumstances. As in the circuit of FIGURE 1, the switching current flows from earth 3 to terminal 11 through either resistor 6 and winding. 4 or resistor 7 and winding 5. Referring to FIGURE 3, the potential applied across the winding 4 or 5 which carries the switching current is maintained at a value equal to the difference between -V,, and V volts. Any'tendency for the potential of the points G, H to rise above V. volts is prevented, any current [flowing through the resistor 6 or 7 in excess of that required for switching the core 8 being diverted through the appropriate diode When switching of the core 8 has been completed, the

- winding 4 or 5 assumes a low impedance and the current illowing through the winding rises appreciably. Under these conditions, and with the contact arm a l in the position shown in FIGURE 3, two currents will flow: firstly a current from earth to terminal 11 through winding 5 of value V /R where R is the resistance of resistor '7, R being of so great a value that the low impedance of wind- 'ing *5 may be neglected; and secondly a current from earth through resistor 45 and diode 12 to the source of potential of -V volts, the value of the current being V /R. Since all the switching current is drawn from earth through resistor 6 or '7, it is clear that the second current just mentioned must at least be equal in value to the switching current required to change the sense of magnetisation in highest to resistors 6, 7 and the intermediate potential to diodes #12, 13. On the other hand, if the diodes 12, 13 are reversed, the highest of the three potentials should be applied to terminal 11, the lowest to resistors 6, 7, and the intermediate potential, as before, to the diodes 12, '13.

I claim:

-1. An electric signal detector comprising a core of magnetisable material having a substantially rectangular hysteresis loop, the core being capable of stability when magnetised either in a first or in a second opposed direction of magnetisation; a first winding inductively coupled with the core in a rfirst sense, and a second winding inductively coupled with the core in a second opposed sense; change-over switching means for connecting the first and responsive means for operating the switching means on the application of a signal thereto and ,for restoring the switch- :ing means on the termination of said signal; the changeover switching means being operable on the application of a signal tothe signal-responsive means to interrupt a (flow of current through the first winding andto establish a tllow of current through the second winding thereby changing the direction of magnetisation of the core, and being. restorable on the termination of said signal to interrupt the flow of current through the second winding and to re-establish the flow of current through the first winding thereby reversingsaid change in the direction of magnetisation of the core; and an output winding inductively coupled to the core at which an output signal is delivered at each change and reversal in the direction of core magnetisation.

it is connected during an operation or restoration of thechange-over switching means. I

3. An electric signal detector as claimed in claim 1, including voltage regulating means connected to that end of each of the first and second windings which isv remote tfrom the change-over switching means.

4. An electric signal detector comprising an electromagnetic relay adapted to be energized during the appli cation of a signal to the detector and to be deenergized I second Iwindingsalternately to a voltage source, signalupon termination of said signal; acore of magnetisable material having a substantially rectangularhysteresis loop, the core being capable of stability when magnetised either in a first or in a second opposed direction of magnetisation; a first winding inductively coupled with the core in a first sense, and a second winding inductively coupled with the core in a second opposed sense; the electromagnetic relay having a change-over contact for connecting the first and second windings alternately to a voltage source, said contact being operable upon en-ergisation of the relay to interrupt a how ofv current through the first winding winding inductively coupled to the core at which an output signal is delivered at each operation or release of the change-over contact; a resistor in series with each of the first and second windings having a resistance large in relation to the impedance assumed by the winding in series therewith during an operationor release of the changeover contact; and voltage regulating means connected to each of the first and second windings at theend of the winding remote from the change-over contact.

5. An electric signal detector comprising a relay having a change-over contact, said relay being adapted to be energised during the application of a control signal to the detector'and deenergised upon termination of said signal; a magnetic core of material having a substantially rectangular hysteresis loop, an output winding inductively'cou pled to the core; and a pair of input windings inductively coupled to the core; the change-over contact of the relay having a pair of fixed terminals each connected to one of the input windings, the input windings being so arranged that the, magnetic field inducedin the core by a current flowing in one of the input windings is reversed by current established in the other input winding on each changeover of the change-over contact, whereby an output signal of significant amplitude is deliveredat the output winding on reversal of the core held and output signals of only relatively insignificant amplitude are delivered subsequently while the change-over contact changed position. i

References Cited by the Examiner UNITED STATES PATENTS 2,811,710 10/57 Demer 340 174 3,033,997 5/62 Salihi 307-.88 IRVING L. SR'AGOW', Primary Examiner. I

JOHN BUR-NS, Examiner. 1

attains stability in its 

1. AN ELECTRIC SIGNAL DETECTOR COMPRISING A CORE OF MAGNETISABLE MATERIAL HAVING A SUBSTANTIALLY RECTANGULAR HYSTERESIS LOOP, THE CORE BEING CAPABLE OF STABILITY WHEN MAGNETISED EITHER IN A FIRST OR IN A SECOND OPPOSED DIRECTION OF MAGNETISATION; A FIRST WINDING INDUCTIVELY COUPLED WITH THE CORE IN A FIRST SENSE, AND A SECOND WINDING INDUCTIVELY COUPLED WITH THE CORE IN A SECOND OPPOSED SENSE; CHANGE-OVER SWITCHING MEANS FOR CONNECTING THE FIRST AND SECOND WINDINGS ALTERNATELY TO A VOLTAGE SOURCE, SIGNALRESPONSIVE MEANS FOR OPERATING THE SWITCHING MEANS ON THE APPLICATION OF A SIGNAL THERETO AND FOR RESTORING THE SWITCHING MEANS ON THE TERMINATION OF SAID SIGNAL; THE CHANGEOVER SWITCHING MEANS BEING OPERABLE ON THE APPLICATION OF A SIGNAL TO THE SIGNAL-RSPONSIVE MEANS TO INTERRUPT A FLOW OF CURRENT THROUGH THE FIRST WINDING AND TO ESTABLISH A FLOW OF CURRENT THROUGH THE SECOND WINDING THEREBY CHANGING THE DIRECTION OF MAGNETISATION OF THE CORE, AND BEING RESTORABLE ON THE TERMINATION OF SAID SIGNAL TO INTERRUPT THE FLOW OF CURRENT THROUGH THE SECOND WINDING AND TO RE-ESTABLISH THE FLOW OF CURRENT THROUGH THE FIRST WINDING THEREBY REVERSING SAID CHARGE IN THE DIRECTION OF MAGNETISATION OF THE CORE; AND AN OUTPUT WINDING INDUCTIVELY COUPLED TO THE CORE AT WHICH AN OUTPUT SIGNAL IS DELIVERED AT EACH CHANGE AND REVERSAL IN THE DIRECTION OF CORE MAGNETISATION. 